Direct positive emulsions containing iodide ions and a sensitizing dye

ABSTRACT

Preparation of silver halide emulsions by (a) adding 5-15 mg. per mole of silver halide of a water-soluble inorganic iodide to an aqueous redispersion of a precipitated, ripened and washed, water-permeable colloid silver chlorobromide or bromide emulsion, and (b) adjusting the pH to 5-9 and digesting the emulsion at 110* to 150* F. for about 15-60 minutes, there being added per mole of silver halide 0.00033 to 12.0 g. of an amine borane as a fogging agent; characterized in that after the digesting step, there is added per mole of silver halide approximately 10-100 mg. of an optical sensitizing dye.

I Umted States Patent [151 3,647,455 Burt et a1. 45 M 7, 1972 [54] DIRECT POSITIVE EMULSIONS 3,367,780 2/1968 Fix.... ..96/107 X CONTAINING IODIDE IONS AND A ento SENSITIZING DYE 3,501,309 3/1970 Gilman ...96/107 X [72] Inventors: Cortland Russell Burt; Peter Anthony 3,501,312 Mee ---96/ 07 X Ciavarri, both of Ro h t r, NY, 3,505,070 4/1970 Litzerman ..96/ 107 X [73] Assignee: E. I. du Pont de Nemours and Company, p,ima,yExamine, John1- Goolkasian wllmmgton Assistant Examiner-M. E. McCamish 22 Filed: O 3 1 Att0rneyLynn Barratt Morris [21] App]. No.: 865,976 [57] ABSTRACT Preparation of silver halide emulsions by (a) adding -15 mg. [52] US. Cl ..96/64, 96/663, 96/ 101 per mole of silver halide of a water-soluble inorganic iodide to [51] Int. Cl ..G03c 1/36 n que r i p n f a pr p ripened n [58] Field of Search 96/64, 663, 95, 99, 100, 107 washed, water-permeable colloid silver chlorobromide or bro- 9 101 110 mide emulsion, and (b) adjusting the pH to 5-9 and digesting the emulsion at 1 10 to F. for about 15-60 minutes, there 56] References Cited being added per mole of silver halide 0.00033 to 12.0 g. of an amine borane as a fogging agent; characterized in that after UNITED STATES PATENTS the digesting step, there is added per mole of silver halide approximately 10-100 mg. of an optical sensitizing dye. 3,249,440 5/1966 Hunt ..96/108 7 Claims, No Drawings DIRECT POSITIVE EMU-LSIONS CONTAINING IODIDE IONS AND A SENSITIZING DYE CROSS-REFERENCES TO RELATES APPLICATIONS BACKGROUND OF THE INVENTION This invention relates to direct positive colloid silver halide photographic emulsions. More particularly it relates to such emulsions which are prefogged by a chemical fogging agent.

Direct positive emulsions are, of course, well known and there are many different methods of producing direct positive elements. For example, a silver halide emulsion may be given a short overall exposure of high intensity radiation and then given a longer imagewise exposure of lower intensity. Upon development, a direct positive will be obtained. Another method is to expose imagewise and develop and bleach out developed silver and then flash expose and redevelop. A still further method is to chemically fog the silver halide grains with, for example, formaldehyde, hydrazine, sodium arsenite, silver ions and other nonsulfide fogging agents instead of using a solarizing exposure. Upon lmagewise exposure and development of such chemically fogged elements, a positive image is obtained. 1n direct positive photographic elements utilizing this latter method, there is usually incorporated a desensitizing compound, usually a colored desensitizing dye. A significant improvement was made in the art by the use of amine boranes as chemical fogging agents in direct positive emulsion systems. Direct positive emulsions and elements comprising such emulsions are described and claimed in Bigelow & Burt, U.S. Pat. No. 3,361,564 and in Assignees Burt, U.S. Pat. No. 3,445,235. This latter patent discloses and claims the use of rhodium and iridium salts as antikink agents in direct positive emulsions described in the above patent. The direct positive emulsions made as described in Bigelow 8L Burt U.S. Pat. No. 3,361,564, and the Burt patent are extremely fast as compared to direct positive elements of the prior art and suffer none of the disadvantages of long exposure times, low reversal densities, undesirable stain due to desensitizing dyes, as well as undesirable contrast, and a multiplicity of exposure steps and processing operations.

SUMMARY OF THE INVENTION It has now been found that the speed of the direct positive emulsions disclosed and claimed in Bigelow & Burt U.S. Pat. No. 3,361,564 and Burt U.S. Pat. No. 3,445,235 can be increased 8-20 times by the process of manufacture described hereinafter.

This invention provides a process for preparing a direct positive photographic silver halide emulsion which may contain minor amounts of silver chloride, which comprises:

a. admixing with each mole of silver halide approximately -15 millimoles of a water-soluble inorganic iodide, preferably sodium, potassium, or ammonium iodide, to a redispersion in an aqueous medium of a precipitated, ripened and washed silver chlorobromide or silver bromide emulsion that is preferably free from water-soluble salts, and

b. adjusting the pH to approximately 5-9 and digesting the emulsion at 110 to 150 F. for about to about 60 minutes, there being added during adjusting or digesting of the emulsion per mole of silver halide from 0.00033 to 12.0 g. of an amine borane as a fogging agent;

characterized in that after the digesting step is essentially complete, there is added, per mole of silver halide, approximately 10-100 mg. of an optical sensitizing dye.

After the optical sensitizing dye is added, the pH of the emulsion is adjusted to between 5.0 and 7.0 with a suitable adjuvant, e.g., citric acid or sodium hydroxide and the usual coating aids, e.g., gelatin, hardeners, surfactants, etc., are added and the emulsion is coated on a support and dried in a conventional manner. As will be seen in the examples under the preferred embodiment there is a synergistic effect as indicated by increased speed from the combination of iodide added at the beginning of the digestion period and an optical sensitizing dye added at the end of the digestion period.

PREFERRED EMBODIMENT While any of the silver halides conventionally used in photographic emulsions may be used it is preferable in the process of this invention to precipitate silver chloride in an acid colloid medium and then add a soluble bromide in sufficient amount to convert substantially all of the silver chloride to silver bromide. While the range of amine boranes which may be added is from 0.00033 to 12.0 grams per mole of silver halide, the preferred amount is from 0.013 to 1.3 g. It is advantageous to add 1.5 to 325 mg. of a rhodium salt and/or an iridium salt per mole of silver halide, as taught by the above Burt application.

To demonstrate the fact that there is a synergistic effect from the combination of adding a soluble iodide at the beginning of digestion and an optical sensitizing dye at the end of digestion the examples set forth below have four parts. Part (a) has neither iodide nor optical sensitizing dye added thereto. Part (b) shows the effect of adding an iodide salt at the beginning of digestion but no optical sensitizing dye at the end of digestion. Part (c) shows the effect of adding only the dye at the end of digestion and Part (d) shows the synergistic effect of adding the iodide salt at the beginning of digestion and an optical sensitizing dye at the end of digestion.

The sensitometric characteristics of the direct positive emulsion may be determined by processing test strips of the coated layer in the following manner. A test strip of the following examples is fixed out in a conventional photographic fixer to provide a means of establishing the minimum density (D Test strips are exposed in an intensity scale sensitometer (described on page 616, Mees, The Theory of the Photographic Process. MacMillen Company, New York, 1942) using a [2 step wedge and Log E of 5.71. The exposed strips are developed for 1 /2 minutes at 68 F. in a developer having the composition:

Water ml 750 Metnl g. 1.5 Sodium sulfitc (anhydrous) g. 19.5 Hydroquinone g. 6.0 Sodium carbonate (anhydrous) g. 24.0 Potassium bromide g. 0.8

Water to make 10 liter The developed strips are then immersed in a conventional short stop for 5 to 10 seconds, fixed for 3 minutes in a conventional fixer, and then washed and dried.

ln evaluation of the processed strips, the minimum density (D equals the lowest density above that of the fixed out strip mentioned above. The maximum density is the highest density above D,,,,-,,. The speed is expressed in terms of /EXO. The speed of a typical commercial direct positive in terms of 100/EX10 is 10.3 and said material has a D,,,,-,, of 0.01 and a D of 4.5.

From emulsion-coated elements prepared according to this invention good duplicates can be made by contact-printing, using either carbon arc lamps or tungsten photofloods as a light source. The elements may be used for reproducing continuous tone negatives, half-tones, line copy, engineering drawings, etc. The direct positive elements of this invention may also find use in color photography.

Optical sensitizing dyes other than those disclosed below may be used, either acid or nonacid and the art is replete with useful dyes.

Although gelatin is the colloid carrier most used in the photographic manufacturing art other carriers for the silver halide crystals may be used. For example other natural and synthetic water permeable colloid binding agents may be used. Such agents include water-permeable or water-soluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, and acetals containing a large number of CH CHOH groups; hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable colloids of the last-mentioned type are disclosed in U.S. Pat. Nos. 2,276,322; 2,276,323; and 2,396,866. The useful polyvinyl acetals include polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid bind ing agents include the poly N-vinyl-lactams of Bolton, U.S. Pat. No. 2,495,918, the hydrophilic copolymers of N- acrylamido alkyl betaines described in Shacklett, U.S. Pat. No. 2,833,050 and hydrophilic cellulose ethers and esters.

The emulsions made bygthe process of this invention may be coated on any suitable base including paper and transparent film supports. For example, the cellulose supports, e.g., cellulose acetate, cellulose triacetate, cellulose mixed esters, etc., may be used. Polymerized vinyl compounds, e.g., copolymerized vinyl acetate and vinyl chloride, polystyrene, and polymerized acrylates may also be mentioned. The film formed from the polyesters made according to the teachings of Alles, U.S. Pat. No. 2,779,684 and patents referred to in the specification of that patent. Other suitable supports are the polyethylene terephthalate/isophthalates of British Pat. No. 766,290 and Canadian Pat. No. 562,672 and those obtainable by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyclohexane -l,4-dimethanol (hexahydro-p-xylene alcohol). The films of Bauer, et al., U.S. Pat. No. 3,059,543 may also be used. The above polyester films are particularly suitable because of their dimensional stability. The emulsions are generally coated on the supports in quantities to give a coating weight of about 50-75 mg. of silver halide per square decimeter of support surface area.

Many amine boranes other than those disclosed in the examples may be used, including those disclosed in the Bigelow et al., U.S. Pat. No. 3,361,564. A practical limit is imposed upon the use of certain boranes due to toxicity and possible explosive characteristics of the individual boranes.

The invention will now be further illustrated in and by the following examples.

EXAMPLE I To an acidified aqueous solution of gelatin containing 1 :50

then ripened by heating for minutes at 160 F. A second addition of potassium bromide in an amount of 0.6 mole was added and'the resulting direct positive silver chlorobromide emulsion was ripened for 10 minutes at 160 F.

The resulting emulsion was coagulated, washed and redispersed in the manner disclosed in Moede, U.S. Pat. No. 2,772,165, issued Nov. 27, 1956. The temperature of the redispersed emulsion was raised to 130 F. and there was then added 87 g. of gelatin, and the pH adjusted to 6.0 with sodium hydroxide. There was then added 2.70 mg. of morpholine borane. The emulsion was divided into 4 parts and labeled (a), (b), (c) and (d). Part (a) was digested at 130 F. for 40 minutes. A gelatin hardener was added and the emulsion was coated on a photographic film support and dried in a conventional manner. Part (b) was treated as above except that 6.67 millimoles of potassium iodide per mole of silver halide was added at the start of digestion. Part (c) was treated as 1(a) except that at the end of digestion there was added 33.34 milligrams of the optical sensitizing dye 4( l,3,4-trimethylindolidi nyl) ethylidene-(3-methyl-l-p-sulfophenyl)-5-pyrazolone of the formula:

Part ((1) was treated as in Part (21) except that at the beginning of digestion there was added 6.67 millimoles of potassium iodide and at the end of digestion there was added 33.34 mg. of the sensitizing dye disclosed above in 1(c). The sensitometric results are shown in the following table as processed in the manner described above.

TABLE I Sample No. Speed l00/EX l 0 D,,,,,, D,,,,,,

1(a) 2490 4.93 0.005 1(b) 5450 4.79 0.04 KC) 5060 4.30 0.16 1(d) 44800 3.61 0.05

The above data clearly show that speed increases are ob- EXAMPLE I] Example I was repeated using 1(a) and 1(b) emulsions as controls which are designated ll(a) and ll(b). To Part "(0), there was added 66.67 mg. per mole of silver halide of the optical sensitizing dye having the formula:

Part ll(d) was treated as described in 1(a) except that the amount of potassium iodide disclosed in I(b) was added before digestion and the amount of optical sensitizing dye shown above was added after digestion. The sensitometric results are shown in the following table when processed as described above.

TABLE II The above data show that synergistic speed increases are obtained when the iodide and optical sensitizing dye are added in the above manner.

EXAMPLE in Example 1 wasrepeated using 1(a) and 1(b) as controls but designated as lll(a) and [ll(b). To Part Ill(c), there was added just after digestion 66.67 mg. per mole of silver halide of the optical sensitizing dye having the formula:

Part lIl(d) was treated as described in 1(a) except that the amount of potassium iodide disclosed in 1(b) was added just before digestion and the amount of optical sensitizing dye shown above was added just after digestion. The sensitometric results are shown in he following table when processed as described above.

The above data clearly shows the synergistic speed effects.

EXAMPLE lV Example 1 was repeated using 1(a) and I(b) as controls and designated lV(a) and [V(b). To Part lV(c) there is added 66.67 mg. per mole of silver halide of the sensitizing dye having the formula:

on, "H

\CCH=OHCH=C/ Q N N Part lV(d) was treated as described in 1(a) except that the potassium iodide disclosed in 1(b) was added before digestion and 66.67 mg. of the optical sensitizing shown above was added just after digestion. The sensitometric results are shown in the following table when sample strips were processed as described below.

TABLE IV Example 1 was repeated except that in place of 2.70 mg. of morpholine borane there were added 133.34 mg. of

trimethylamine borane as the chemical fogging agent. The sensitizing dye used was the same at that shown in Example ll(c). The sensitometric results are shown in the table.

Sample No. l00/EX10 Speed D. D.,,.

Wu) 5450 4.00 0.13 V(b) 9940 4.00 0.19 V(c) 43300 2.18 0.15 V(d) 72500 4.50 0.17

EXAMPLE Vl Example I was repeated except that 83.34 mg. per mole of silver halide of the dye having the following structure was added at the end of the digestion period.

The sensitometric results are shown in the following table.

Example ll was repeated using 1(a) and l(b) as controls which are designated Vll(a) and Vll(b). The emulsion was divided into 8 portions and the (c), (d), (e), (f), (g), and (h) portions containing the addition of 66.67 mg. of the optical sensitizing dye as described in Example ll also contained varying amounts of potassium iodide as shown in the following table.

Example 11 was repeated except that in place of 2.7 mg. of morpholine borane there was added 2.70 mg. of tertiary butyl amine borane per mole of silver halide. The emulsion was divided into 4 parts and designated (a), (b), (c), and (d). Sample Vlll(a) contained neither iodide nor optical sensitizing dye. Sample Vlll(b) contained 13.34 millimoles of potassium iodide per mole of silver halide added just prior to digestion and Sample Vlll(c) was the same as (a) only with the addition just after digestion of 66.67 mg. of the optical sensitizing dye of Example 11 per mole of silver halide. Sample Vlll(d) was the same as (a) except that 13.34 millimoles of potassium iodide was added just before digestion and 66.67 mg. was added just after digestion. The sensitometric results are shown in the following table when processed as described in Example 1.

2 TABLE VIII The data of Table Vlll show the synergistic speed effects obtained via dye and iodide addition in a direct positive emulsion chemically fogged with tertiary-butylamine borane.

As is evident from the sensitometric data set forth in the above tables the process of this invention provides direct positive elements having extremely high speeds as compared to commercial direct positive material of the prior art as described, above. The direct positive elements prepared by the process described here also have high maximum densities and very low minimum densities. The elements may be developed in standard developing solutions using standard techniques. Variations in the developing solution will have much the same effect as it would in developing nonreversal emulsions. No preexposure operations or auxiliary processing procedures are necessary or desirable using elements made by the process of this invention. It is unnecessary to use desensitizing compounds as is commonly done in the direct positive art. The amine boranes as chemical fogging agents are far superior to formaldehyde, the principle fogging agent of the prior art, because the borane compounds do not have any hardening effect on the gelatin layer. As indicated above, any of the amine boranes listed in Bigelow & Burt US. Pat. No. 3,161,564, Jan. 2, 1968, can be used. Preferred alkyl amine boranes have the formula:

wherein R is an alkyl radical of 1-20 carbon atoms, and R and R are each taken from the group consisting of H and alkyl of 1-20 carbon atoms.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for preparing a direct positive photographic silver halide emulsion whichcomprises a. adding approximately 5-15 millimoles of a water-soluble inorganic iodide. per mole of silver halide to a redispersion in an aqueous medium of a precipitated, ripened and washed water-permeable colloid silver chlorobromide or bromide emulsion, and adjusting the pH to approximately 5-9 and digesting the emulsion at 110 to 150 F. for about 15-60 minutes, there being added during the adjusting or digesting of the emulsion per mole of silver halide 0.00033 to 12.0 g. of an amine borane as a'fogging agent; characterized in that. after the digesting step is essentially complete, there is added per mole of silver halide approximately 10-100 mg. of an optical sensitizing dye.

2. A process according to claim 1, wherein the colloid is gelatin.

3. A process according to claim 1, wherein the sensitizing dye is 4(1,3,3-trimethylindolidinyl) ethylidene-( 3-methyll -psulfophenyl)-5-pyrazolone.

4. A process according to claim 1, wherein the sensitizing dye is 2(3-ethyl thiazolylidene) ethylidene-3 carboxymethyl- 5-rhodanine.

5. A process according to claim l, wherein the sensitizing dye is 4(p-dimethylbenzal) 3-methyl-l-p-sulfophenyl-5- pyrazolone.

6. A process according to claim 1, wherein the sensitizing dye is 3,3(2-carboxyethyl)-5,6,5,6 tetramethyl benzoxazole carbocyanine.

7. A process according to claim 1, wherein the amine borane is an alkyl amine borane of the formula 1?: Rr-IIVBH Ra 40 wherein R, is an alkyl radical of l-20 carbon atoms, and R,

and R are each taken from the group consisting of H and alkyl of l-ZQcarbon atoms. 

2. A process according to claim 1, wherein the colloid is gelatin.
 3. A process according to claim 1, wherein the sensitizing dye is 4(1,3,3-trimethylindolidinyl) ethylidene-(3-methyl-1-p-sulfophenyl)-5-pyrazolone.
 4. A process according to claim 1, wherein the sensitizing dye is 2(3-ethyl thiazolylidene) ethylidene-3 carboxymethyl-5-rhodanine.
 5. A process according to claim 1, wherein the sensitizing dye is 4(p-dimethylbenzal) 3-methyl-1-p-sulfophenyl-5-pyrazolone.
 6. A process according to claim 1, wherein the sensitizing dye is 3,3''(2-carboxyethyl)-5,6,5'',6'' tetramethyl benzoxazole carbocyanine.
 7. A process according to claim 1, wherein the amine borane is an alkyl amine borane of the formula wherein R1 is an alkyl radical of 1-20 carbon atoms, and R2 and R3 are each taken from the group consisting of H and alkyl of 1-20 carbon atoms. 